Optical signatures of a fully dark exciton condensate

TL;DR

This paper introduces optical techniques to detect and analyze dark exciton condensates, which are otherwise invisible through photoluminescence, by examining absorption shifts and polarization effects caused by dark-bright exciton interactions.

Contribution

It presents novel optical methods to identify dark exciton condensates and determine their properties through absorption blueshift and polarization analysis.

Findings

Dark exciton density can be measured via absorption blueshift.

Polarization dependence reveals the condensate's polarization state.

Faraday effect can detect dark exciton presence without photoluminescence.

Abstract

We propose optical means to reveal the presence of a dark exciton condensate that does not yield any photoluminescence at all. We show that (i) the dark exciton density can be obtained from the blueshift of the excitonic absorption line induced by dark excitons; (ii) the polarization of the dark condensate can be deduced from the blueshift dependence on probe photon polarization and also from Faraday effect, linearly polarized dark excitons leaving unaffected the polarization plane of an unabsorbed photon beam. These effects result from carrier exchanges between dark and bright excitons.